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Mikrokĥimeraisùm
。不過，具體的機制到現在還是不太清楚。 懷孕期間，由於母體及胎兒的免疫細胞有機會透過在胎盤進行的血液透析而進行交換，被交換的細胞在宿主內仍有可能會繼續分裂，並在胎兒出生後的數十年後依然留在宿主體內。 }} Types of microchimerism In humans (and perhaps in all Placentals) the most common form is fetomaternal microchimerism (or fetal chimerism) whereby immune cells (mostly T and B lymphocytes, monocytes, macrophages and NK cells) from a fetus pass through the placenta and establish cell lineages within the mother. Fetal cells have been documented to persist and multiply in the mother for several decades After giving birth, about 50-75 % of women carry fetal immune cell lines. Maternal immune cells are also found in the offspring yielding in maternal→fetal microchimerism, though this phenomenon is about half as frequent as the former . Microchimerism had also been shown to exist after blood transfusions to a severely immunocompromised population of patients who suffered trauma. Relationship with autoimmune diseases and breast cancer Microchimerism has been implicated in autoimmune diseases. Independent studies repeatedly suggested that microchimeric cells of fetal origin may be involved in the pathogenesis of systemic sclerosis. Moreover, microchimeric cells of maternal origin may be involved in the pathogenesis of a group of autoimmune diseases found in children, i.e. juvenile idiopathic inflammatory myopathies (one example would be juvenile dermatomyositis). Microchimerism has now been further implicated in other autoimmune diseases, including systemic lupus erythematosus. Contrarily, an alternative hypothesis on the role of microchimeric cells in lesions is that they may be facilitating tissue repair of the damaged organ. Moreover, fetal immune cells have also been frequently found in breast cancer stroma as compared to samples taken from healthy women. It is not clear, however, whether fetal cell lines promote the dvelopment of tumors or, contrarily, protect women from developing breast carcinoma. Microchimerism and disease within the context of a tripartite conflict A recent hypothesis interprets this relationship by considering fetal, maternal, and paternal adaptive interests separately and in interaction with one another. Theoretically, fetuses may benefit from immunological information gathered by their migrant immune cells in the maternal body provided that many of them return into the fetus. They may also benefit from improved maternal defense, provided that fetal cell lines (carrying partly paternal resistance alleles) contribute to maternal defense against pathogens or tumors. However, fetuses may be jeopardized by a selfish maternal usage of fetomaternal microchimerism – i.e. some mothers get pregnant only to improve their immune system and then to abort. The use of microchimeric cells by the maternal immune system may contribute to the adaptive benefits of female choosiness and polyandry. While fathers may enjoy an indirect benefit from enhanced fetal and maternal health, they also face the risk of wasting their sexual efforts due to selfish pregnancies of cheating females. Paternal alleles acting via clones of microchimeric cells in the maternal body could launch an immunological attack against the non-kin sperm in the female genitalia, or against the non-kin fetus in the womb. Thus microchimeric cells carrying partly the alleles of a former father may launch an attack on a new embryo fathered by a new male. Furthermore, an intraspecific version of Zahavi’s Mafia Hypothesis could explain a potential interaction between the abortion of fetuses and a subsequent rise of an autoimmune disease. This hypothesis suggests that males may be capable to provoke microchimerism-induced autoimmune-like diseases in the mother in revenge of selfish pregnancies. This hypothetic paternal threat could increase the maternal costs associated to selfish pregnancies, thus reduce the chance that males just waste their efforts. According to the traditional medical thinking, autoimmune disease may cause infertility, habitual abortion and miscarriage. However, this interpretation does not explain why autoimmune diseases (at least several types of them) occur mostly in women, and cannot explain why abortion tends to precede the rise of autoimmune problems. On the contrary, considering the tripartite immune conflict among the fetus, the mother and father as realized by means of a two-way traffic of immune cells through the placenta can nicely explain these phenomena. See also / Si osou / 參看 * 嵌合體 * 腎移植 * 自體免疫 References / Riförènses / 參考 Category:醫學 Category:Autoimmune diseases Category:Diseases and disorders Category:Reproduction Category:Mating Category:Evolutionary biology Category:Sexual selection